Accounts suggest the initial confrontations started when England fans reacted to unprovoked attacks by groups of local youths, which were exacerbated by alcohol. French police then stepped in and deployed tear gas.

According to French prosecutors, 150 Russians "well prepared for ultra-rapid, ultra-violent action" were involved. There are claims "ultras" - hardened hooligans - from both Russia and France went to the tournament intent on targeting England fans.

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Clashes broke out at the end of the match between England and Russia

Some British fans complained that the "heavy-handed" police approach escalated the situation. But the behaviour of England fans has been criticised too.

Home Secretary Theresa May described the violence as "deeply disturbing" and said some England fans had let their country down by getting involved in the disorder, which also saw fist-fighting and bottles thrown.

Among those arrested so far are Britons, French, Russians and an Austrian. In a much smaller incident in Nice, about a dozen Northern Ireland supporters retaliated to what police said was an unprovoked attack by French hooligans.

How did it unfold?

About 35 people have been injured in the disorder - four seriously - and 20 people arrested.

Thursday 9 June - Before the first match of the tournament had even begun, trouble was brewing off the field. In the early hours of Friday morning, exuberant chanting by England fans outside a pub in the Old Port district of Marseille turned into drunken confrontations with local youths and French riot police. One England fan and a local man were arrested

Friday 10 June - In the build up to England's first match with Russia in Marseille, police again deployed tear gas and a water cannon in an attempt to quell clashes between England, France and Russia supporters. One Briton was seriously hurt

Saturday 11 June - As the 1-1 draw between England and Russia at the Stade Velodrome drew to a close, a number of Russia fans set off flares. TV footage showed a group of Russians charge towards England supporters, many of whom fled by climbing over fencing. Meanwhile in Nice, six Northern Ireland fans were injured in a clash with France fans outside a bar

Sunday 12 June - Uefa warned it would kick England and Russia out of the tournament if there were further violent scenes. It announced charges against Russia - but not England - for the stadium incident, but admitted there were security issues

Monday 13 June - About 150 "well-prepared" Russian hooligans were behind the Marseille stadium violence, French prosecutors said. Police "spotters" began analysing footage to identify culprits involved in all incidents. The French government urged host cities to ban alcohol near venues to prevent further violence

To what extent was the disorder orchestrated?

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Some Russia supporters had smuggled in flares which they set off at the end of the match

The stadium attacks were planned and perpetrated by "well-trained" Russian hooligans, according to Marseille prosecutor Brice Robin.

Witnesses at the game described seeing men who had "come prepared" for trouble with gum shields and gloves used for martial arts. Some British newspapers have reported that Russian "firms" issued threats to England fans well before the tournament.

Russian sports journalist Ivan Kalashnikov says many Russian fans "live under the impression that hooliganism is still a big thing in Europe and in England".

"They wanted to make an impression. It's for the Russian authorities to speak to them and make them understand there is no hooligan competition going on. There were known leaders [among the 150 stadium attackers], even though the Russian authorities banned some known hooligans from travelling."

Meanwhile, violence by England fans has largely been attributed to drunken aggressiveness rather than organised hooliganism.

British police issued about 1,400 banning orders against known hooligans from England, Wales and Northern Ireland to prevent them from travelling to the tournament, and British police hooligan "spotters" have been deployed in France.

Who are the Russian hooligans?

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Russia's hooligan fringe learned much of what they know from the English hooliganism of the 70s and 80s - but they are a new and different breed, according to journalist Andrei Malosolov, co-founder of Russia's Fans' Union.

"Now many people are boxers or into mixed martial arts, and Russian hooligans often follow a very healthy way of life, avoiding alcohol which used to be part of the subculture," he says.

They use choreographed tactics, and wear logos identifying their allegiance, and footage of clashes is posted online. Many of the larger Russian "firms" have websites of their own.

"Delegations" of hooligans were sent from towns little known outside Russia like Orel and Krasnodar, reports from France suggest. Fans say key members of the bigger firms, including two linked to Moscow teams CSKA and Spartak, were banned from travelling.

What action has been taken against those responsible?

Russia has been given a suspended disqualification from the championships and a 150,000 euro (£119,000) fine for disorder at the game against England.

Uefa warned Russia will be kicked out of the tournament if their fans commit any further violence inside a stadium. It has also promised to strengthen security and fan segregation following Saturday's incident.

England has also been threatened with disqualification if there is further trouble, prompting an appeal for calm from England manager Roy Hodgson and captain Wayne Rooney.

Other fans implicated in the disorder are expected to be dealt with in the coming days.

What else is being done to stop the trouble and will it work?

The French police

Along with making arrests, French police reacted to some of the more serious disorder by using tear gas and water cannon.

But some fans have complained they were heavy handed and they have also been criticised over their policing strategy.

The UK and French governments

The French government has urged host cities to ban alcohol near venues. There will be a 24-hour drinking ban in Lens before the England game.

The UK government has said it will deploy British police officers trained in football disorder to France ahead of the Wales match. Additional British Transport Police officers will also be deployed on rail services around the area.

Downing Street has offered to send police "spotters" to sit in the crowd at the next match.

It said British officers would be assisting the French with their post-incident investigations after Marseille and that Border Force presence at ports in the UK had been enhanced.

What is the mood among fans?

Fans of all nationalities have described feeling both saddened by what has happened, and afraid for their safety.

Alberto, from Italy, told BBC Newsbeat the trouble in Marseille was horrible, adding: "I feel scared being here now, I was scared to come here to Nice because we're close to Marseille."

Others have complained about "slack" security. Artur, from Poland, said: "Security is very, very poor."

"We're going to Marseille in less than two weeks for Poland against Ukraine and to be honest I'm a little bit afraid," he says. "We are afraid of the organisation at this tournament because look at Saturday, there was no segregation between the Russian and English fans.

Where do fans go next?

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Up to half a million supporters of England, Wales and Northern Ireland are expected to travel to France for the Euros

An estimated 350,000 to 500,000 supporters from the UK are expected to travel to France for matches throughout the course of the tournament, according to police. But not all spectators will have tickets - there were about 250,000 tickets sold to UK residents from 1.6m applications.

There are some concerns that Lille may present another flashpoint for violence, as Russia and England fans may once again be in close proximity.

Russia's next match against Slovakia will take place in Lille on Wednesday - the day before England's match against Wales, just 24 miles away in Lens. England fans had been advised to stay in Lille because Lens is a small city.

Football Association chairman Greg Dyke has expressed "serious concerns" about security in Lille.

Northern Ireland play Ukraine in Lyon on Thursday. A full match schedule can be found here.

Should fans worry about going to matches?

The Foreign Office has issued safety advice for those travelling to matches in France - it warns fans to drink responsibly, or face being barred from venues or fan zones.

Neither the British police nor the UK government say it is unsafe to go, but UK fans have been warned that French police will not tolerate drunken or anti-social behaviour.

"Troublemakers will be dealt with by French police in line with their laws and can expect a banning order on return to the UK," said Mark Roberts, the National Police Chiefs' Council lead for football policing.

British police plan to act as "cultural interpreters" to prevent heavy-handed tactics against drunk and rowdy fans who may not cause serious trouble.